Could any of you inform me of the knife head balls I have shown. I got them when I purchased my mower and wonder if they all will work with my sicklebar seems they are different lengths and/or styles. The longest ones are 14 3/8" while the shortest is 11 1/4". Not sure how many teeth are on the bar. 20? And lastly is it necessary to have 1 1/2 tooth cutter on the tip?

MA139 is an older version of the part. MC139 is the latest version I know of. Note that the MA139 has the older IHC logo cast into it. Either will work on the knife for a Cub mower. Your top one is bent. The middle one looks like it has been run with loose rivets.

The double or triple sections at the end weren't even on the early mowers. They can be used or not, are helpful in some mowing conditions.